The ability to respond to various intracellular and/or extracellular stresses allows
April 19, 2017
The ability to respond to various intracellular and/or extracellular stresses allows the organism to adapt to changing environmental conditions and drives evolution. an organelle with a wide array of fundamental functions most notably the harvesting of energy from food and the control of cell death. We compare UPRmt with the extensively characterized KN-62 cytosolic warmth shock response (HSR) and the unfolded protein response in endoplasmic reticulum (UPRER) and discuss the current knowledge about UPRmt signaling pathways as well as their potential involvement in COL4A5 physiology. (Pellegrino et al. 2013 Worm strains expressing a GFP reporter fused to promoters of the mitochondrial chaperones HSP-6 and HSP-60 (homologs of mammalian mtHSP70 and HSP60 respectively) were used to evaluate the activation of the UPRmt pathway. The temperature-sensitive strain which conditionally activates UPRmt has been isolated by ethyl methanesulfonate (EMS) mutagenesis but its molecular target remains obscure (Benedetti et al. 2006 However in most studies specific manipulations that all trigger proteotoxic stress in KN-62 the mitochondria have been used to induce UPRmt experimentally. Paraquat treatment leading to excessive production of reactive oxygen varieties (ROS) activates UPRmt (Runkel et al. 2013 Additionally UPRmt can be induced by inactivation of multiple genes implicated in the mitochondrial protein-handling machinery such as by RNAi of PQC protease paraplegin/(complex IV) (complex III) and (ubiquinone synthesis) also induces UPRmt (Baker et al. 2012 Durieux et al. 2011 These manipulations deplete solitary components of particular OXPHOS complexes and presumably overload the mitochondrial chaperones with their respective partner proteins which cannot be put together into multiprotein complexes. KN-62 UPRmt signaling in gene and activates its transcription. Presumably the UBL-5 and DVE-1 complex cooperates with ATFS-1 to activate chaperone manifestation but the mechanism of this connection has not been investigated. As the closest DVE-1 homologs in mammals KN-62 are the global chromatin organizers SATB1 and SATB2 (Dobreva et al. 2003 Yasui et al. 2002 the DVE-1/UBL-5 complex in might mediate chromatin redesigning in order to facilitate ATFS-1 access to chaperone promoters. The crosstalk between UPRmt and UPRER in has recently been recognized (Baker et al. 2012 Inhibition of cytosolic translation by phosphorylation of eIF2α is one of the main reactions during ER stress mediated by PERK (Harding et al. 1999 Downregulation of protein translation in the cytosol was also recognized during mitochondrial proteotoxic stress (Baker et al. 2012 Within the context of UPRmt general control non-repressed 2 (GCN-2) kinase and the GLC7-like phosphatase (GSP-1) alter the phosphorylation status of eIF2α (Fig. 1). Under mitochondrial unfolded protein stress GCN-2 phosphorylates eIF2α and thus inhibits protein translation in the cytoplasm which sequentially reduces the folding weight on mitochondrial chaperones (Baker et al. 2012 The GCN-2-mediated phosphorylation was shown to be dependent on ROS generated in dysfunctional mitochondria. As ATFS-1 and HAF-1 activities are not required for eIF2α phosphorylation GCN-2 is definitely defined as a player of a parallel complementary protecting pathway in UPRmt rules. Additionally phosphoinositide 4-kinase (PIFK-1) has been suggested to act in the signaling of both UPRmt and UPRER triggered by ROS inducer paraquat; however its mechanism of action in these pathways has not yet been investigated (Runkel et al. 2013 UPRmt signaling in mammals In mammals the UPRmt signaling mechanism has been investigated in cell tradition models by ethidium bromide treatment KN-62 (Martinus et al. 1996 and overexpression of aggregation-prone mutant protein ornithine transcarbamylase (OTC) targeted to the mitochondrial matrix (Zhao et al. 2002 Several components of the pathway such as the mitochondrial chaperones and the quality control protease ClpP were shown to be conserved from (Baker et al. 2012 dsRNA-activated protein kinase (PKR) also known as eukaryotic translation initiation element 2-α kinase 2 (EIF2AK2) mediates phosphorylation of eIF2α therefore attenuating protein translation in the cytosol during UPRmt in mammalian systems (Fig. 2) (Rath et al. 2012 Interestingly PKR together with ClpP is also required.